trophic control Argentina 4 Asteroidea 4 Coastal eutrophication 4 El Nino-Southern Oscillation 4 Helianthus 4 Heliaster helianthus 4 Herbivory 4 Nutrients 4 Peru 4 Predation 4 Rocky intertidal 4 San Antonio Bay 4 Semimytilus algosus 4 Starfish 4 Tidal influence 4 Top-down vs. bottom-up controls 4 Ulva 4 Ulva lactuca 4 abundance 4 accumulation rate 4 algae 4 algal bloom 4 bioaccumulation 4 biomass 4 bivalve 4 colonization 4 community dynamics 4 echinoderm 4 environmental disturbance 4